Many skin treatment devices require contact between an active area of the device and the skin for reasons of safety and/or efficacy.
For example, in light-based hair removal systems, the light energy is typically delivered through a transparent surface that makes contact with the skin. In such systems, the active area of the device is the light-emitting surface, and contact between this surface and the area of the skin to be treated is desirable both to ensure good transmission of the light to the treatment area, and, depending upon whether the device is otherwise eye safe, to aid in eye safety by eliminating stray light that might pose an eye hazard. At the same time, it is desirable to provide a system which does not require that the light-emitting surface be pressed into the skin to such a degree that the skin deforms.
Other examples of treatment devices that require skin contact include (1) devices that require contact only to prevent light leakage, such as a UV illuminator that requires no skin cooling but has a contacting baffle to prevent stray light, or (2) devices that require contact only for their mechanism of action and not to prevent light leakage, such as a thermal heater that delivers a pulse of heat through direct conduction to the skin. Other dermatological devices and methods that involve skin contact include ultrasound and radio frequency applications, such as wrinkle reduction. Some dermatological devices and methods provide skin contact through an interface material, such as ultrasound gel, oil, water, or index matching fluid. It is to be understood that these devices and methods are still considered to be skin contacting for the purposes of this application.
A significant problem for such devices is that the operator may angle or tilt the device's applicator such that it is not substantially perpendicular to the skin. This can create the situation where the entire surface of the active area is not in contact with the skin, and therefore the objective of efficacy and, for those devices which are not otherwise eye safe, will not be achieved.
Another problem for light-based devices is to ensure that the light-emitting surface is contacting a surface appropriate for treatment rather than, for example, eyeglasses. Typical contact sensors would generally sense positive contact if an applicator was applied to a person's eyeglasses, creating a potential for emission directly into the eye that, for many devices, could lead to serious injury or blindness. A similar condition could be created with household window panes or other similar transparent surfaces, whereby a contact sensor could sense contact against the window and light could be dangerously emitted into the ambient environment. It is desirable, therefore, for a dermatologic contact sensor not to be activated by eyeglasses or similar surfaces, but preferably only by a surface suitable for treatment.
A review of the state of the art shows that the existing devices and methods have important deficiencies. In particular, the existing designs do not solve the problem described above where the device applicator is applied at an angle and do not properly detect skin. While various mechanical systems exist which attempt to prevent dangerous emissions, most mechanical devices are complicated, costly and unreliable, as well as other shortcomings. A key advantage of capacitive sensing is its inherent imperviousness to ESD damage since no direct electrical connection to the skin is required. Although not necessary for capacitive sensing, it is possible to insulate the sensors of a capacitive sensor with a thin, electrically insulating, dielectric material.
Thus, there is a clear need for a practical contact sensor for skin treatment devices that would detect skin contact and also ensure skin contact across the entire active area of the device.